Patterns of the Moon and Stars
Students will be thinking about patterns that exist outside our Earth in the coming weeks!
Please read this background information from our Stemscopes Curriculum to guide your home conversations!
We can observe and record how the Moon’s appearance changes each month. The Earth and Moon waltz together around a common point, their center of mass, called the barycenter. From our perspective, however, it looks like the Moon orbits the Earth. The Moon goes through a cycle of phases about once every 29 ½ days. These phases are caused by our seeing more or less of the Moon’s sunlit side. This occurs because the relative positions of the Sun and Moon change each day in our sky. Starting when the Sun and Moon are closest in the sky, New Moon, it takes about 1 week for us to see the Moon become a crescent (waxing crescent) and proceed to being half lit (first quarter – always lit on the right side). During the next week it becomes more than half full (waxing gibbous). About two weeks after it was new, the moon is full. During the next two weeks, we see less and less of the lit side, reversing the order of phases through waning gibbous, third quarter (always lit on the left side), waning crescent, and finally back to new moon. At all times, we are seeing the Moon because of sunlight scattered off its surface. This cycle of patterns allowed ancient cultures to create lunar (Moon phase-based) calendars that signaled times to fish, hunt, plant, and harvest. These calendars also formed the basis for the 30-31 day month used today.
Note: Students do not need to know the names of the Moon phases, but the names may help them remember the cycle of phases. They do, however, need to know that the phase shapes follow a pattern. It is hard to detect the change in the Moon’s phase over a period of just 1 day. Also, explain to students that the Moon rises approximately one hour later each night. This means that only the first two weeks of Moon phases are visible during early evening. Weeks 3 and 4 of Moon phases are only visible late at night or too early in the morning to catch. The Moon is up all night only when it is full. On every other day, the Moon is visible for some time during the day. Encourage your students to look for it in the daytime sky! They can see phases during the day or during the night.
No one should ever look at the Sun directly for more than a fraction of a second. Doing so will cause eye damage. Having said that, note that we can observe and record how the Sun appears to change position in the sky throughout the day. It is easiest to do that around sunrise and sunset. This is best done by observing the changing length and direction of an object’s shadow during different times of the day.
Ancient people worshipped the Sun for heat and light, but feared winter, when the lack of Sun brought death and despair. Today we know the Earth rotates, giving the illusion that the Sun rises in the east and sets in the west. The Sun also appears to move in a curved, rather than a straight, line as it slowly moves from east to west.
Lengths of shadows cast by the Sun vary throughout the day. Because the pattern is repeated each day, shadows were used to tell time. This eventually led to the use of the sundial. When the Sun is low on the horizon, objects cast long shadows. When the Sun is high in the sky, objects cast the shortest shadows.
When our side of the Earth rotates so that the Sun is up in our sky (daytime), the air scatters sunlight and turns the sky a blue color. At night when the Earth turns away from the Sun, our planet blocks the Sun’s light and the air on a cloudless night is transparent, so we can see the stars. Humans make patterns out of their points of light, like dot-to-dot pictures that seem to slowly move across the sky in big curves, just like the Sun. This apparent movement of the Sun and stars is caused by the Earth’s rotation. The stars do move in space and relative to each other, but they are all so far away that these motions are not detectable over a human lifetime without using high technology.
Stars are actually present in the daytime sky, too. However, the air scatters so much sunlight and hence is so bright that these dim points of light can’t be seen. Also, bright city lights scatter so much light in the sky at night that overwise visible, dimmer stars are invisible when you are in or near cities. If students want to watch for these amazing star patterns, they will need to find a place without much human-made light. That is the reason astronomers put telescopes on top of mountains, far away from city lights.
-Stemscopes Curriculum
